Phylogenomics of bonytongue fishes (Osteoglossomorpha) shed light on the craniofacial evolution and biogeography of the weakly electric clade (Mormyridae)

Bonytongues (Osteoglossomorpha) constitute an ancient clade of teleost fishes distributed in freshwater habitats throughout the world. The group includes well-known species such as arowanas, featherbacks, pirarucus, and the weakly electric fishes in the family Mormyridae. Their disjunct distribution, extreme morphologies, and electrosensory capabilities (Notopteridae and Mormyroidea) have attracted interest by many, yet a comprehensive phylogenetic framework for comparative analysis is missing. We provide a phylogenomic analysis of 179 species (out of 260), 28 out of 29 genera, and all six families of extant bonytongues and find that the interfamilial relationships support previous molecular phylogenies. However, we find pervasive misalignment between the phylogeny and mormyrid taxonomy. Based on a recent reassessment of the fossil record of this group, we inferred dates of divergence among trans-continental clades and the major groups. The estimated ages of divergence for the major clades (e.g., Osteoglossomorpha, Osteoglossiformes, Mormyroidea) are older than previous reports, but most of the divergences of clades on separate continents are too young to be explained by biogeographic vicariance hypotheses. Ancestral state estimations of craniofacial phenotypes reveal pervasive convergence which may have contributed to taxonomic confusion. Biogeographic analysis of the Pan-African distribution of mormyrids indicates that their high species diversity in the Congo Basin is a consequence of range reductions of widespread ancestors. Finally, our results show that the highest diversity of craniofacial morphologies among mormyrids originated in the Congo Basin, suggesting niche partitioning of morphological and electrosensory adaptations of this uniquely diverse clade.